Addressing Class Imbalance with Latent Diffusion-based Data Augmentation for Improving Disease Classification in Pediatric Chest X-rays

Deep learning (DL) has transformed medical image classification; however, its efficacy is often limited by significant data imbalance due to far fewer cases (minority class) compared to controls (majority class). It has been shown that synthetic image augmentation techniques can simulate clinical variability, leading to enhanced model performance. We hypothesize that they could also mitigate the challenge of data imbalance, thereby addressing overfitting to the majority class and enhancing generalization. Recently, latent diffusion models (LDMs) have shown promise in synthesizing high-quality medical images. This study evaluates the effectiveness of a text-guided image-to-image LDM in synthesizing disease-positive chest X-rays (CXRs) and augmenting a pediatric CXR dataset to improve classification performance. We first establish baseline performance by fine-tuning an ImageNet-pretrained Inception-V3 model on class-imbalanced data for two tasks-normal vs. pneumonia and normal vs. bronchopneumonia. Next, we fine-tune individual text-guided image-to-image LDMs to generate CXRs showing signs of pneumonia and bronchopneumonia. The Inception-V3 model is retrained on an updated data set that includes these synthesized images as part of augmented training and validation sets. Classification performance is compared using balanced accuracy, sensitivity, specificity, F-score, Matthews correlation coefficient (MCC), Kappa, and Youden's index against the baseline performance. Results show that the augmentation significantly improves Youden's index (p<0.05) and markedly enhances other metrics, indicating that data augmentation using LDM-synthesized images is an effective strategy for addressing class imbalance in medical image classification.